A continual goal of ink jet printing is the achievement of printed images having improved visual quality. As is known in the art, a number of specific criteria dictate the visual quality of an image, such as chroma, optical density, and edge acuity. Overall image quality is determined by the permanence of such visual characteristics over time, and in view of various environment-imposed stress. Examples of image permanence characteristics include the ability of an image to resist fading upon exposure to light and atmospheric gasses and pollutants, (i.e. light fastness and air fastness), as well as the ability to resist damage upon exposure to humidity (waterfastness) or mechanical abrasion (i.e. smear resistance). Moreover, image resistance to physical abrasion is an important indicator of image permanence.
In addition to the above-recited image quality characteristics, an ink composition must meet a number of other criteria in order for the ink composition to be suitable for use as an ink jet ink. For example, the ink must not clog the ink jet printer nozzles, which have tight tolerances, typically 30 to 40 um in diameter. Further, the ink must not create a buildup of residue on the resistor elements that are responsible for firing the ink out of the nozzles. Such resistor elements are typically subjected to several hundred million firings over the life of an ink cartridge, and fouling of the resistor elements by a build up of ink residue, known as kogation, degrades pen performance and reduces the commercial life and value of the resistor.
The improvement of various aspects of ink jet ink compositions is a continually ongoing effort. Two attributes affecting permanence and image quality that have recently received significant attention are water fastness and smear resistance. This focus is especially pertinent for certain printing applications that must endure a higher risk of exposure to moisture and physical abrasion, such a bar code and photo quality printing.
To this end, a number of attempts have been made to improve the waterfastness, and smear resistance of a printed ink jet image. Various compositions and mechanisms that purport to increase the permanence of a printed ink jet image are known. However, most of these mechanisms and compositions contain one or more significant drawbacks, such as the requirement for special print media, various ingredient combinations that reduce ink jet pen reliability, and chemicals that are hazardous to human health, which require the use of a warning label and special shipping and handling conditions.
As a result, ink compositions and imaging methods that provide a highly water fast and smear resistant image, in a safe and consistent manner, without compromising the image's initial visual qualities, and which meet the performance criteria for use in an ink jet printer, continue to be sought through ongoing research and development efforts.